San Antonio Mayor Julián Castro, a rising star in the Democratic Party, got most of the attention at the White House Friday afternoon when President Barack Obama announced him as the new choice for secretary of Housing and Urban Development.

But Shaun Donovan, the outgoing HUD secretary, will be the one with more power during the last two-and-a-half years of Obama’s time in the White House.

Donovan, the nominee to take over the Office of Management and Budget, won’t have a huge public profile, but will be key in shaping Obama’s legacy and advancing a progressive agenda through federal regulations.

Current and former administration aides see Donovan’s appointment as directly fitting into the larger turn to executive authority that’s been led by Obama counselor John Podesta — and potentially, if Podesta leaves the White House next year as he’s promised, a potential heir to leading that effort for the remainder of Obama’s term.

Especially before the 2012 election, the White House slowed many regulations due to political fears. But with his “pen and phone” strategy, Obama’s been looking to move forcefully around Congress, and Donovan sees himself as an aggressive, progressive addition.

Other OMB directors “said no,” Donovan told Obama upon being offered the job, according to a person familiar with the conversation. “That’s not who I am. I’m going to find ways to do things, not to not do things.”

There’s a lot he’ll have the opportunity to do, from digging in on the renewed attention to Environmental Protection Agency regulations — OMB already has been reviewing the draft standards limiting carbon dioxide emissions on existing power plants and EPA will release those standards June 2, with a final version due in June 2015 — to the long-pending executive order banning LGBT discrimination among federal contractors.

More EPA rules are expected as part of the continuing rollout of Obama’s Climate Action Plan put out next year, and OMB will be at the center of signing off on all of them. But the emissions standards are the most significant, with the potential to either be arguably the biggest single measure the nation’s taken to address climate change — but require not being so oppressive that they put plants out of business while not being so loose that they’re totally ineffectual.

Even more complicated politically will be the executive actions on immigration that Obama’s expected to announce over the summer if the White House’s waning last hope for a pre-midterms deal with the House falls through. Homeland Security Secretary Jeh Johnson is currently conducting a review to make recommendations, with White House input, but any decision — to further alter the administration’s approach to deportations, for example — would eventually route through Donovan at OMB.

Obama senior adviser Dan Pfeiffer also has met with allies on the Hill and among progressive groups in recent weeks, soliciting ideas for new executive orders and actions.

All of that will put Donovan eagerly in the center, the newest addition to the president’s inner circle at the White House.

“He is a progressive who will be in a place to get progressive things done,” said one person familiar with Donovan’s record.

That’s the management part of the job. The budget part is going to be even trickier.

“In an ordinary situation where there were lots of decisions to be made and the president was eager to make them, it would be a powerful place to be,” said Alice Rivlin, one of President Bill Clinton’s OMB directors. “Right now, there isn’t much budget action and there probably isn’t going to be because of the two year Ryan-Murray agreement and the general gridlock situation.”

Those paying attention to Donovan’s approach still see an opportunity — even without new resources appropriated, to have big and lasting impacts.

“There’s still a budget that needs to get done for FY 2015,” said the source familiar with the Donovan process. “And for FY 2016, do we return to sequester, or do we find a way to make smarter choices, find savings, particularly around our Tax Code? Are there opportunities to try to get an agreement that goes beyond Murray-Ryan?”

Administration officials declined public comment ahead of the formal nominations.

Donovan will take over for Sylvia Mathews Burwell, who, if confirmed as expected, will be the new Health and Human Services secretary. Generally well-regarded and well-liked within the White House, she’s credited with helping navigate the administration through the shutdown and leading the negotiations over the Murray-Ryan deal — the closest Washington’s come to a working budget in years.

Donovan isn’t part of the small circle of Democratic budget experts who’ve dominated OMB throughout the Obama years and going back to the Clinton administration, but he does have a reputation for being a wonk, and that only got more intense at HUD. Taking a page from his old boss, former New York City Mayor Michael Bloomberg, for whom he served as housing commissioner before joining the Cabinet, he’s made data a central part of every decision, even creating a “HUD-Stat” modeled on the New York Police Department’s famous CompStat system.

“It’s connecting the data to a way to really drive policy,” the source said. “One of the biggest problems in government and bureaucracies is that people don’t know what success looks like.”

Donovan took a similar approach in getting to a $26 billion, 2012 mortgage settlement between all the biggest lenders and every state attorney general, and coordinating the administration’s response to Hurricane Sandy, both in the immediate cleanup and investing proactively around the country in resilience protections against future storms. Administration officials also credit him for helping to create a centralized process that streamlined the freeing up and allocation of existing resources in a way that got more money out more quickly than people in Washington or Detroit were expecting.

“Shaun’s earned a reputation as a great manager, a fiscally responsible leader, and somebody who knows how the decisions we make here in Washington affect people’s lives around the country,” Obama said at the White House, officially announcing the nomination.

As he took the microphone at the event, Donovan joked about not being able to compete for star power.

”Try going between Barack Obama and Julián Castro,” he said.

But he made clear that he’s looking for a clear, strong role within the White House.

“As the president said last year, the budget is not just about numbers. It’s about our values and our future,” Donovan said.

Of course, OMB directors don’t operate alone, but in tandem with the National Economic Council staff. But those who’ve been through the process, including on the Obama staff, say that Donovan will have the opportunity to show imagination in implanting or initiating new ideas.

All of this will put him in constant negotiations with both Republicans and Democrats, but that’s an area where Donovan has a stronger record of success than many others within the administration.

Joking with people about his outreach at HUD, Donovan likes to joke about working for Bloomberg, a Democrat-turned-Republican-turned-independent.

“I worked for all three parties, and that was just under one mayor in New York,” he tells people.